Nanoengineered and Biomimetic Protein-derived Adhesives with Improved Adhesion Strength and Water Resistance

  • Author / Creator
    Bandara, Nandika P.
  • The oilseed industry generates a great deal of meal after oil extraction. Soy meal has a number of value added applications while canola meal is used mainly as a low-value animal feed. There is a growing interest on value addition of meal beyond feed uses. Canola and soy meal contain ~ 33-37% and 43-47% (w/w on DM basis) of protein, respectively. As protein-rich biomass, there is a potential to develop protein-based adhesives as an alternative to petrochemical based adhesives. However, protein based adhesives suffer from weak water resistance and adhesion that limit their widespread commercial applications. Nanomaterials are widely used in composite research to improve flexural strength, elasticity, and thermal stability, while biomimetics are used in biomedical field to develop improved materials by mimicking natural materials as a model. Therefore, the overall objective of this research was to develop protein based adhesive with improved adhesion and water resistance using oilseed proteins via nanotechnological and biomimetic approaches. Two hypotheses were tested in this research: (1) exfoliating nanomaterials in canola protein and preparing hybrid adhesives with chemically modified canola protein will improve adhesion and water resistance; (2) biomimetic modification of soy protein to impart 3,4-dyhydroxyphenylalanine groups will improve adhesion and water resistance. In the first study, exfoliating nanomaterials in canola protein at 1% (w/w) increased the dry, wet and soaked adhesion strengths from 6.38 ± 0.84, 1.98 ± 0.22, and 5.65 ± 0.46 MPa (control sample) to 10.37 ± 1.63, 3.57 ± 0.57, and 7.66 ± 1.37 MPa (nanocrystalline cellulose - NCC) and 8.14 ± 0.45, 3.25 ± 0.36, and 7.76 ± 0.53 MPa (graphite oxide - GO) respectively. Nanomaterial induced increase in thermal stability, exposed hydrophobic groups due to secondary structural changes, and nanomaterial induced cohesion were responsible for the improved adhesion. In the second study, effect of different oxidation levels of GO on adhesion was studied. Increasing oxidation time decreased C/O ratio while relative proportion of C-OH, and C=O groups initially increased up to 2 h of oxidation, but reduced upon further oxidation. Canola protein-GO hybrid adhesive (CPA-GO – with 1% GO (w/w) addition) prepared with 2 h oxidized GO increased (p < 0.05) dry, wet and soaked strength to 11.67 ± 1.00, 4.85 ± 0.61, and 10.73 ± 0.45 MPa respectively. Improved exfoliation of GO, improved adhesive and cohesive interactions, increased hydrogen and hydrophobic interactions and improved thermal stability of CPA-GO contributed towards the improved adhesion. In the third study chemically modified canola protein-nanomaterial (CMCP-NM) hybrid wood adhesives were developed. Modifying canola protein with ammonium persulphate (1% w/w APS/protein) significantly improved (p < 0.05) adhesion to 10.47 ± 1.35, 4.12 ± 0.64 and 9.39 ± 1.20 MPa for dry, wet and soaked strength respectively. Exfoliating 1% NCC into CMCP further improved adhesion to 12.50 ± 0.71, 4.79 ± 0.40, and 10.92 ± 0.75 MPa while 1% GO increased the adhesion to 11.82 ± 1.15, 4.99 ± 0.28, and 10.74 ± 0.72 MPa for dry, wet and soaked strength respectively. In the fourth study randomly oriented strand boards (ROSB) were produced using nanoengineered canola protein adhesive (CPA) at pilot scale. The mechanical performances, bond durability and water resistance were not affected by CPA addition up to a level of 40%, compared to commercial LPF adhesives. Mechanical performance of all ROSB panels exceeded the acceptable minimum standards specified by CSA O437.0-93 standards; therefore it can be used in commercial ROSB production, either as 100% resin for interior application or up to 40% replacement of LPF for exterior applications. In the fifth study, mussel inspired biomimetic soy protein adhesive was developed by converting inherent amino acids tyrosine into 3,4-dihydroxyphenylalanine (DOPA) by reacting with tyrosinase followed by adding NaOH and FeCl3. Adhesion was significantly increased from 4.97 ± 0.94, 1.79 ± 0.52, and 5.62 ± 0.65 MPa to 13.21 ± 1.58, 3.93 ± 0.21, and 12.10 ± 0.46 MPa for dry, wet and soaked strength respectively, mainly due to DOPA mediated polymerization and crosslinking, increased cohesive interactions, and hydrophobic interactions with wood surface. In addition, prepared adhesive showed acceptable adhesion to mica, glass and polystyrene surfaces as well. The findings of this thesis provide evidence on the potential of nanotechnological and biomimetic methods to develop protein based adhesives with improved adhesion and water resistance.

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    Doctor of Philosophy
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